High performance drum brake assembly for automotive braking system

ABSTRACT

A High performance drum brake assembly design is developed which can substantially increase the brake output torque for a given hydraulic input pressure or reduce the required pipeline pressure to realize the current rated torque. The brake assembly has a new lever ( 17 ) pivoted on the leading shoe ( 19 ) web with one end resting on the wheel cylinder piston ( 11 ) and the other end on the strut assembly ( 15 ). This lever touches the piston instead of the leading shoe web and receives input from the pressurized wheel cylinder. The lever rotates about its pivot point ( 18 ) and pushes the strut assembly. The trailing shoe ( 3 ) receives two inputs, one from the wheel cylinder and the other from the strut assembly. The wheel cylinder input and the strut reaction force together acting on the pivot, results in almost twice the force acting on the leading shoe.

FIELD OF INVENTION

This invention in general pertains to automobile technology. Moreparticularly this invention pertains to automotive braking system. Inparticular, this invention relates to the design of a new drum brakeassembly for automotive braking purposes.

At the outset of the description, which follows, it is to be understoodthat the ensuing description only illustrates a particular form of thisinvention. However, such particular form is only an exemplaryembodiment, and without intending to imply any limitation on the scopeof this invention.

PRIOR ART

It is to be noted that the prior art description gives detailinformation of the technology, method, process and system known in theart, it explains the deficiency in the related art and the object of theinvention being to overcome or surmount the problem associated with theprior art. This forms the essential feature and the object of theinvention.

With continuous improvement in engine technology, better roads,increasing cruising speeds and stringent statutory/regulatoryrequirements, there is an inherent need to develop safer braking systemsto meet this requirement. Also, to cater to the increasing vehicleweights, increasing speeds and to offer improved braking performance,hydraulic drum brake assemblies have increased in size from φ7″ to φ12″to date catering to the passenger car and utility vehicle applications.

Attempts to provide a good braking system resulted in providing betterfriction material and bigger diameter drum brakes predominantly for rearapplications. Consequences to the above proposal are addressing brakesqueal, consistency in brake lining performance, grabbing tendency,early morning sharpness, high fade, high lining wear and biggeractuation systems respectively.

Along with the increased cost associated with the above proposals,packaging bigger brakes within the available wheel size has always beena problem. To address the above issues, the current designs are studiedand a new proposal is given which can overcome the above problems.

Besides increase in wheel cylinder and brake diameter, duo-servo designhas been developed to increase the service & parking brake performanceto cater to the requirement. Sensitivity of the duo-servo design tochanges in friction level has put limitations on wide acceptance to thisdesign.

With increasing wheel cylinder and brake diameters growingproportionately to meet the requirements, associated problems ofincreasing actuation requirements and packaging poses immense problems.Pedal effort reduction is also achieved either by increasing frictionlevel or decreasing master cylinder size (notwithstanding impact onpedal travel) for a given braking system.

To address the above issues, a drum brake assembly is designed which cansubstantially increase the brake output torque for a given hydraulicinput pressure or reduce the required pipeline pressure to realize thecurrent rated torque compared to the conventional design.

This design as explained in the following section overcomes all theabove constraints in meeting friction level, pedal efforts, cost andpackaging requirements while also providing all the features of a drumbrake.

As such for novelty of the invention, the published information in USAand European patents has been accessed and a list of sample cited patentdocuments given below cover the following patent specifications:

A cited PCT/US patent application having patent no WO 96/07833 datedMar. 14, 1996 filed by HINO JIDOSHA KOGYO KABUSHIKI KAISHA relates to aninvention having a rod set up in the inner surface of the rim toeffectively reduce the screeching of a brake.

A cited European patent application having patent no 95306755 dated Sep.25, 1995 filed by Ford Motor Company relates to an invention of a massdamper for attenuating objectionable noise.

A cited European patent application having patent no 95106211 dated Apr.25, 1995 filed by Nisshinbo Industries Inc relates to an invention of acoloured strip for visual indication of the brake lining wear.

A cited PCT/US patent application having patent no WO 96/16275 dated May30, 1996 filed by TOKYO BUHIN KOGYO CO LTD., relates to an invention ofsetting up different natural frequencies for the two shoes to reduce thepossibility of a screeching sound.

A cited PCT/US patent application having patent no 6513632 dated Feb. 4,2003 filed up TRW Automotive relates to an invention of an actuator withan electric drive motor and an electronic unit for parking brakeactuation.

A cited PCT/US patent application having patent no 4646885 dated Mar. 3,1987 filed by FORD Motor Company relates to an invention of a dual drumbrake assembly to generate an enhanced brake torque.

A cited US patent application having patent no 4332311 dated Jun. 1,1982 filed by Toyota Jidosha Kogyo Kabushiki Kaisha, JP relates to aninvention of a shoe hold down, device in a drum brake.

A cited PCT/US patent application having patent no WO 92/20938 datedNov. 26, 1992 filed by Automotive Products plc relates to an inventionof an adjuster comprising a lever member and pawl member mounted on onebrake shoe with a bimetallic strip to prevent adjustment at elevatedtemperatures.

On perusal of the cited documents with respect to our invention, it hasbeen found prima-facie that our invention is unique and distinct fromthe cited inventions.

This invention, therefore, proposes a drum brake assembly for automotiveapplications, which has various objectives such as to furnish a greaterbraking force, than normally possible, to handle higher speeds, largersizes and greater vehicle weights, without any abnormal change in thedimensions or weight associated with the normal, known drum brakeassembly.

Further objects and advantages of the invention will become apparentfrom consideration of the drawings and the ensuing description.

The foregoing description of outlined rather broadly preferred andalternative feature of the present invention so that those skilled inthe art may better understand the detailed description of the inventionthat follows. Additional features of the invention will be describedhereinafter that forms the subject of claims of the invention. Thoseskilled in the art should appreciate that they can readily use thedisclosed conception and specific embodiment as a basis for designingand modifying other structures for carrying out the same purposes of thepresent invention. Those skilled in the art should realize suchequivalent conception do not depart from the spirit and scope of theinvention in its broadest form.

SUMMARY OF INVENTION

The inventors have made great effort to provide a system, which meetsthe requirement of the industry and overcome the problem associated inthe prior art.

To achieve the above object according to first aspect and feature of thepresent invention, a system is provided by which the unutilized space onthe leading shoes near the wheel cylinder is utilized so as to enhancethe utility of the drum brake assembly for automotive braking system.

According to second aspect and feature of the invention in addition tothe first feature of the invention, comprises the utilization of spaceby employing an additional lever arrangement and connected in such wayto the existing lined shoe in order to increase the brake output torquefor a given pipe line pressure compared to identical drum brake design.

Further objects of the invention will be clear from the ensuingdescription.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are intended to provide for the understandingof invention, incorporating in and constitute a part of invention. Thedrawings illustrate on embodiment of invention and together with thedescription illustrate principle of invention. The drawings are given byway of non-limitative example to explain the nature of the invention.

For complete understanding of the invention, reference is now made tothe following description taken in conjunction with the accompanyingdrawings.

This invention will now be described in further detail with reference tothe accompanying drawings which are illustrated in:

FIG. 1: Shows elevation of the known drum brake assembly

FIG. 2: Shows an embodiment of the elevation of the proposed drum brakeassembly, by way of example and not by way of limitation, of the scopeof this invention

FIG. 3: shows a schematic Sketch of the forces acting in the known drumbrake assembly

FIG. 4: shows a schematic sketch of the forces acting in the highperformance drum brake design

FIG. 5: shows a 3D model of the high performance drum brake assembly

FIG. 6: shows the 3D back view model of the high performance drum brakeassembly

FIG. 7: shows a 3D model of the close-up view of the new leverarrangement on the lined leading shoe assembly

FIG. 8: shows a 3D model of the links used for the ADAMS analysis.

FIG. 9: shows a graph giving the input-output relationship of theconventional design and the High Performance design during dynamometertest at 25 kph equivalent vehicle speeds.

FIG. 10: shows a graph giving the input-output relationship of theconventional design and the High Performance design during dynamometertest at 50 kph equivalent vehicle speed.

FIG. 11: shows a graph giving the input-output relationship of theconventional design and the High Performance design during dynamometertest at 75 kph equivalent vehicle speed.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION

FIG. 1 illustrates the conventional drum brake now In use:

The drum brake assembly consists of a backplate (1), lined leading shoe(2), lined trailing Shoe (3), wheel cylinder assembly (4), strutassembly (5), handbrake lever (6), shoe hold down springs (7,8) and shoereturn springs (9,10). The wheel cylinder assembly (4) is bolted to thebackplate (1) and the lined leading shoe (2), lined trailing shoe (3)are assembled onto the backplate with the help of shoe hold down springs(7,8) and shoe return springs (9,10). When the wheel cylinder assembly(4) is pressurised, pistons (11,12) in the wheel cylinder (4) push thelined leading shoe (2) and lined trailing shoe (3), overcoming the shoereturn springs (9,10) force and press the lined leading shoe (2) andlined trailing shoes (3) against the rotating brake drum. The drag forcedeveloped at the lined leading shoe (2) and lined trailing shoe (3)shoes against the brake drum slow down the wheel. When the pressure isremoved, the shoe return springs (9,10) aid the retraction of the linedleading shoe (2) and lined trailing shoe (3), back to their normal(released) position and the wheels get free.

FIG. 2 illustrates the High Performance Drum brake assembly of theinvention:

It is known in the art that the conventional drum brake assembly has alinear input-output relationship and amplification is attempted eitherby increasing the wheel cylinder diameter, friction level or the brakediameter per se. The salient feature of the invention is to provide anew lever on the leading shoe web whereby the output from the drum brakeassembly can be enhanced. The invention envisages utilization of thespace on the leading shoe web near the wheel cylinder and connected insuch a way to the lined shoe to increase the brake output torque.

In order to incorporate this idea of space utilization in the existingdrum brake assembly, a structural modification has to be effected inleading shoe web, the change details described are as follows:

The design of high performance drum brake assembly is illustrated in theFIG. 2 of the drawings. An additional new lever (17) is pivoted on thelined leading shoe (19) with one end resting on the wheel cylinderpiston (11) and the other end on the strut assembly (15). This new lever(17) touches the wheel cylinder piston (11) instead of the lined leadingshoe (19) and receives input from the pressurized wheel cylinderassembly (4).

The female push rod (20) of the strut assembly (15) is relieved at theentrance to take in the lined leading shoe (19) and the new lever (17)width at the entrance.

The new lever (17) is pivoted on the lined leading shoe (19) with oneend resting on the wheel cylinder assembly (4) piston (11) and the otherend on the strut assembly (15). This new lever (17) touches the wheelcylinder assembly (4) piston (11) instead of the lined leading shoe (19)and receives input from the pressurized wheel cylinder assembly (4).

Upon actuating the wheel cylinder assembly (4), the new lever (17)rotates about its pivot (18) point and pushes the strut assembly (15).The lined trailing shoe (3) now receives two inputs viz., one from thewheel cylinder assembly (4) and the other from the strut assembly (15),which is mechanically actuated by the new lever (17). The reaction fromthe lined trailing shoe (3) is passed via the strut assembly (15) as anInput to the lined leading shoe (19). The wheel cylinder assembly (4)input and the strut assembly (15) reaction force together acting on thepivot (18), results in almost twice the force acting on the leadingshoe. The combined force from the wheel cylinder assembly (4) and thereaction from the strut assembly (15) acting on the pivot (18) pointachieve equilibrium of the new lever (17). This brake design needs tohave an auto-adjuster mechanism in place and should be operated throughhandbrake mechanism or through the service brake during pressurerelease.

FIGS. 3 & 4 show the input forces from the wheel cylinder assembly (4)acting on the lined leading shoe (19) and lined trailing shoe (3) forthe known drum brake assembly and the high performance drum brakeassembly.

FIGS. 5,6 and 7 show the 3D models of the high performance drum brakeassembly indicating assembly of various parts constituting the inventeddrum brake assembly. FIG. 6 depicts the assembly of the new lever in thebrake assembly. FIG. 7 gives the close-up view of the lever arrangementon to the lined leading shoe assembly.

To validate the principle, a simple link model representative of thedrum brake assembly is simulated using the software Adams/View 12.0 andis shown in FIG. 8. The lined leading shoe and lined trailing shoe arerepresented by links 100 and 101 respectively. Having grounded the links100 & 101, the strut (106) is positioned across the links. The new lever(102) is pivoted (103) to the link (100) with one end resting at thewheel cylinder input (104) and the other end resting at the strut inputend (105). The above geometry is built in Adams/View 12.0 for kinematicsimulation to understand the force transfer mechanism.

The new lever (102) is pivoted to the link (100) by means of a revolutejoint (108). For transfer of force from the new lever (102) to the strut(106), a translational joint (109) is provided.

For simulation purposes, an input force is given to the new lever (102)and also to the link (101) as shown. Upon simulation, the output forcesare captured at the joint (108) and along the strut (106) axis.

Compared to the known drum brake design, the Adams simulation alsovalidates our above discussion in terms of force amplification to thelinks 100 and 101. Link (100) receives almost twice the force at thejoint (108) and the link (101) receives force via the strut (106) axisin addition to the wheel cylinder input force (110).

Salient Features of the High Performance Drum Brake Assembly

-   1) The High Performance drum brake assembly for automotive braking    system has an additional lever positioned on the leading shoe web    and touches the wheel cylinder piston.-   2) Compared to a identical design, the High Performance drum brake    assembly gives increased braking torque for a given pipe line    pressure or needs substantially reduced pipe line pressure to    realize the design rated brake torque.

To validate the high performance design, a prototype sample of φ282×50.8mm hydraulic auto-adjust service, forward pull brake with the newfeature was developed for the test purpose. A conventional φ282×50.8 mmhydraulic auto-adjust, service, forward pull drum brake assembly is alsotaken up for testing to compare the differences in brake output torque.The wheel cylinder diameter, friction lining area, friction lining gradeand the test inertia for the conventional and the high performancedesign are maintained identical for the dynamometer test.

Inertia dynamometer test was carried out on the conventional design andalso on the high performance design to compare the input-outputrelationships.

Dynamometer test was carried out at different vehicle equivalent speedsand pressure levels. Hydraulic pressures of 20 bar to 80 bar in steps of10 bar is applied to the drum brake assembly at each speed level and atan initial braking temperature of 80° C. The input hydraulic pressureand the brake output torque at each speed/pressure level is recorded andpresented graphically.

FIGS. 9, 10 & 11 gives the relationship between input hydraulic pressureand the brake output torque for the conventional design and the highperformance design at vehicle equivalents speeds of 50 kph and 75 kphrespectively. For the conventional design, the graph indicating theinput pressure and the output brake torque is shown with a squarelegend. For the same test conditions, the output obtained with the noveldesign is shown with a triangle legend. An average increase of about 60%in brake output torque with the high performance design for the samepressure input can be observed from the test results. Reverse directionperformance was also carried out and an average increase of about 40% inbrake output torque is realized. The increase in output agrees with thetheoretical prediction and the marginal difference is attributed topivot friction loss, drum deflection, friction material sensitivity tospeed, pressure and temperature.

The increase in brake torque with the High Performance design for theabove test parameters is clearly ascribed to the newly developed conceptas explained in the detailed description of preferred embodiment of theinvention.

The output brake torque obtained in the High Performance design issubstantially higher than the conventional brakes.

Generally, when brakes are proposed for heavier applications, the brakesize (diameter) increase to cater to the higher brake torque. However,in view of this newly developed drum brake assembly, as the externaldimensions are retained, compactness in packaging can easily beaddressed.

While the above description contains many specificities, these shouldnot be construed as limitations in the scope of the invention, butrather as an exemplification of one preferred embodiment thereof. Theterms and expressions in this specification are of description and notof limitation, since there is no intention to exclude any equivalents ofthe features illustrated and described, but it is understood thatvarious other embodiments of this invention is possible, withoutdeparting from the scope and ambit thereof. For example, the invention“High Performance Drum Brake” design needs lower pressure for theexisting brake output torque and hence optimization of wheel cylinderhousing wall thickness is possible. Also, the same design can well beextended to air operated drum brake assemblies to enhance the brakeoutput torque for a given input air pressure.

It is to be noted that the invention “High Performance Drum Brake”delivers brake torque substantially higher than the existing drum brakeassembly, without the necessity of increasing the drum brake size or thewheel size, which results in material savings, cost savings andcompactness in packaging.

Accordingly, the scope of the invention should be determined not by theembodiments illustrated, but by the appended claims and their legalequivalents.

Advantages of the Invention

-   1) The High Performance design extended onto a conventional drum    brake assembly gives increased braking torque for a given pipe line    pressure or needs substantially reduced pipe line pressure to    realize the design rated brake torque.-   2) The High Performance design can be extended to any type/form of    drum brake assemblies currently in existence.-   3) For equivalent design consideration, the High Performance drum    brake design/assembly is compact in terms of packaging.-   4) For equivalent design consideration, the High Performance drum    brake design/assembly can use a low friction linings to deliver the    design rated brake torque.-   5) For equivalent design consideration, the High Performance drum    brake design/assembly can use a smaller wheel cylinder diameter to    deliver the design rated brake torque.-   6) For equivalent design consideration, the High Performance drum    brake assembly can utilize a low friction lining due to the    increased output given by the brake assembly through which a host of    issues such as maintaining lining performance consistency, grabbing,    high fade, noise, early morning sharpness can be easily addressed.

1-12. (canceled)
 13. A high performance drum brake assembly forautomotive braking system, comprises of a cylinder assembly, back plate,strut assembly, lined leading shoe, lined heading shoe and a leverassembly characterized in that the lever is pivotally inclined to thelined leading shoe such that the rear end of the lever is sustained bythe strut positioned at the upper end of the brake drum
 14. The highperformance drum brake assembly according to claim 3 wherein the foreend of the lever is sustained by a piston and a pressurized input issupplied to the lever on actuating the wheel cylinder assembly.
 15. Thehigh performance drum brake assembly according to claim 13, comprisingof a backplate, lined leading shoe, lined trailing shoe, shoe returnsprings, handbrake lever and shoe hold down springs wherein on actuatingthe wheel cylinder assembly the lever rotates about its pivot andactuates the strut assembly so as that lined trailing shoe receivesinputs from both the wheel cylinder and strut assembly.
 16. The highperformance drum brake assembly, as claimed in claim 15, wherein, strutassembly actuates the lined trailing shoe that in-turn actuates thelined leading shoe such that resultant force acting on the leading shoeis atleast twice that of the input and results in low friction lining.17. The high performance drum brake assembly according to claim 15wherein the wheel cylinder is fixed to the backplate by means ofmounting screws and the lined shoe assemblies are held to the backplateby means of shoe hold springs that are held together with the help ofshoe return springs.